I could run my entire system on a 120GB SSD. That's OS, programs, swap, and cache, and probably my current working set of images. In practice I use another 120GB SSD for some data, that way I can take images of my OS SSD with Macrium Reflect for fast backup and restore.
Images don't need to go on an SSD, a good quality spinning disk is fine. A spinning disk transfers data fast enough for processing, given the thumbnails and such are on a cache on the SSD. Yes an SSD will transfer the images faster, but I don't think you're going to get any real world speedup that a human would notice. I actually keep my images on a software mirrored RAID system, two 4TB HGST drives, using Windows storage spaces.
Sometimes buying a Dell/HP/Lenovo will be your best bet on a budget. On the other hand buying a recent generation i5/i7 (i5 is plenty fast for interactive work, i7 is faster for export / video), the lowest model of a good brand motherboard that has the ports you need, 16GB RAM, an SSD, and all the other bits like case, cooling, good quality PSU can sometimes be competitive - just more work and more risk.